Geodesic
Geometric Aspects of Knot Modification of B-spline Surfaces
Journal for geometry and graphics, Tome 6 (2002) no. 2, pp. 141-15 
M. Hoffmann; I. Juhasz. Geometric Aspects of Knot Modification of B-spline Surfaces. Journal for geometry and graphics, Tome 6 (2002) no. 2, pp. 141-15. http://geodesic.mathdoc.fr/item/JGG_2002_6_2_a3/
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     author = {M. Hoffmann and I. Juhasz},
     title = {Geometric {Aspects} of {Knot} {Modification} of {B-spline} {Surfaces}},
     journal = {Journal for geometry and graphics},
     pages = {141--15},
     year = {2002},
     volume = {6},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/JGG_2002_6_2_a3/}
}
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Voir la notice de l'article provenant de la source Heldermann Verlag

In a recent publication we described the effect of knot modifications of B-spline curves. The aim of this paper is the generalization of these results for surfaces. Altering one or two knot values of a B-spline surface, the paths of the points of the surface are discussed first, among which special ruled surfaces can be found. Then we prove that the family of B-spline surfaces obtained by knot alteration, possesses an envelope which is a lower order B-spline surface. Keywords: B-spline surfaces, knot modification. Classification1: 53A05, 68U05.